Tea is the second most consumed beverage after water, and the drinking of tea can be traced back for at least 50 centuries. On a yearly basis around three thousand million kilograms of tea are produced every year. All of this tea consumption has a large impact upon human health and tea is known to have many health benefits mainly due to its antioxidant capacity; additionally green tea is known to be of benefit as an anti-carcinogenic properties; indeed much medical research is being carried out on the components of green tea that have been shown to kill cancer cells.

Of the tea that is produced the most widely drank is the oxidized black form (78%), the non-fermented green form is mainly consumed in Japan and China (though is becoming more and more popular in the Western world) is consumed by about 20% of the worlds population. The other major form of tea is Oolong, which is mainly drank in Taiwan and accounts for around 2% of all tea consumption.

Tea Polyphenols and Cancer

One of the main health giving components of tea are the polyphenols. These are known to have anti-carcinogenic properties, and the main cancer fighting components of tea vary in the way that it is produced. The non-fermented green tea has Epigallocatechin-3-gallate as the main polyphenol with anti-cancer properties, whereas the fermented black tea has the oxidized theaflavin as the main anti-carcinogen polyphenol.

Due to the manufacturing processes used to produce black and green teas, their polyphenols are very different. These differences are summed up below.

1. Green tea: The catechins account for 30 to 42% of the dry weight of green tea. These are found as four main components:
             A. Epigallocatechin-3-gallate (EGCG)
             B. Epigallocatechin (EGC)
             C. Epicatechin gallate (ECG)
             D. Epicatechin (EC)

2. Black tea: Approximately three quarters of the catechins found in black tea undergo enzymatic transformation due to the fermentation process that oxidizes the polyphenols: this leads to the following main components:

A. Catechins
B. Phenolic acids
C. Flavonols
D. Theaflavins
E. Thearubigins
F. Amino acids
G. other components include Carbohydrates, proteins, minerals, vitamins (including vitamin E), and caffeine.

The next section of the time for coffee and tea web site will take a deeper look into tea polyphenols and tea antioxidants.

References
Cabrera et al (2006). Beneficial effects of green tea - a review. J. Am. Coll. Nutr. 25: 79 to 99
Khan and Mukhtar (2007) Tea polyphenols for health promotion. Life Sciences 81: 519 to 533
Yang and Wang (1993). Tea and cancer: review. Journal of the National Cancer Institute 85: 1038 to 1049.